1. Technical Field
The present disclosure generally relates to compositions for controlling plant parasites and compositions for increasing root growth, more particularly to nucleic acid compositions for controlling nematode disease or increasing root growth.
2. Related Art
Nematodes are a very large group of invertebrate animals generally referred to as roundworms, threadworms, eelworms, or nema. Some nematodes are plant parasites and can feed on stems, buds, leaves, and in particular on roots. One important genus of plant parasitic nematodes is the root-knot nematode (Meloidogyne spp.). These parasitic nematodes infect a wide range of important field, vegetable, fruit and ornamental plants. In 2001 the root-knot nematode was responsible for a loss of US$200.5 million in cotton alone.
Existing methods for treating or preventing root-knot nematode disease include the use of chemicals, pesticides, and fumigants. The use of pre-plant soil fumigants is highly effective in controlling root-knot and other plant-parasitic nematodes. However, the majority of the fumigant-type nematicides are no longer available and are also costly and difficult to apply properly under the prevailing conditions.
Crop rotation has also been used to control nematode disease. Rotating onion, carrot, or lettuce with a nonhost crop such as sweet corn and other grain crops, if economically possible, can be effective in controlling the northern root-knot nematode. Unfortunately, current crop rotations on organic soils are of limited value as most crops grown, including potatoes, beans, celery, lettuce, onion, and carrot are susceptible to disease.
The use of cover crops has also been attempted to control nematode disease. Cover crops grown between the main crops may provide an alternative management strategy. Ryegrain, barley, oats, sudangrass, tall fescue, annual ryegrass, and wheat have been shown to be non- or poor hosts to this nematode. Using cover crops, however, can be costly because the cover crops occupy space that could be used to grow more valuable crops.
Biological control organisms have also been used to try to control nematode disease in crops. Commercially available preparations of biological control organisms are limited in their use to regions that can support the growth of the control organism. Moreover, the outcome of using one organism to control another is unpredictable and subject to a variety of a factors such as weather and climate.
Additionally, the root-knot nematode (RKN) is a leading cause of crop loss due to plant parasitic nematodes. The most important species (M. incognita, M. javanica, M. arenaria, M. hapla, M. chitwoodi) have wide host ranges that limit nonhost rotation options. While several examples of host resistance genes in diverse crops exist, the availability of host plant resistance is substantially limited with appropriate resistance loci lacking for the majority of our crops (Roberts, P. A. 1992. Journal of Nematology 24:213-227). In addition, the resistance is limited to only a few RKN species or populations and some resistance genes are heat-sensitive and thus unsuitable for hot production areas. Another limitation of natural resistance genes is the durability of resistance since resistance-breaking populations of RKN can develop after continuous exposure to resistant cultivars, e.g. root-knot resistant tomatoes.
Accordingly, there is need for compositions and methods for controlling, preventing, or reducing nematode disease in plants.
Still other problems affecting crops relate to poorly developed root systems. Root systems of plants are an important part of a plant, and provide many functions that are vital to plant survival. For example, root systems store nutrients for the plant, filter out toxins, help regulate plant growth, provide an absorptive network for water and nutrients, and provide mechanical structures that support the plant and strengthen the soil. Plants with larger roots have increased growth and increased stress tolerance. Increased or enhanced root growth in crop plants would be particularly advantageous because the increased root growth would increase crop yield.
In perennial crops, increased root growth would increase the regrowth rate, increase the yield potential, and increase the likelihood that plants will survive winter. In annuals, increased root size would ensure yield potential under varying environmental conditions. In root crops, enhanced root growth would mean larger yields.
Existing root stimulators typically include fertilizers or plant hormones that must be mixed or formulated in specific concentrations when applied to the plant or soil near the plant. Over application of such stimulators can have adverse effects on the plants, and under application will not achieve the desired outcome. Additionally, application of plant hormones can have undesired consequences. For example, one plant hormone used as a root initiator is auxin or indole-3-acetic acid (IAA). IAA plays important roles in a number of plant activities, including: development of the embryo, leaf formation, phototropism, gravitropism, apical dominance, fruit development, abscission as well as root initiation.
Thus there is a need for new compositions and methods for stimulating or enhancing root growth or development.